A human heart receives its blood supply from the coronary arteries which branch out and around the heart muscle. Conversely, in a reptile, little or no arterial supply of blood is provided to the heart muscle. Instead, the blood supply is mainly delivered through the inside wall of the heart chamber.
Modifying a human heart to imitate the blood delivery method of a reptile heart is currently being used as an alternative or adjunct to coronary artery bypass graft surgery and coronary balloon angioplasty. Normally, a person can only undergo coronary bypass surgery twice, since the risks will begin to outweigh the benefits after that point. Thus, in the past, a patient who has already had two coronary bypass surgeries was left with no recourse. Others have failed repeated coronary balloon angioplasties, and many persons are not suitable candidates for coronary bypass surgery or coronary balloon angioplasty. These persons likewise are left with no recourse.
Early attempts to imitate the reptilian condition in mammals, known as transmyocardial revascularization (TMR), consisted of producing tiny channels in mammalian and human hearts with needles or hot wires. This method met with limited success since, although the channels closed by clotting at the outside surface of the heart, due to exposure to air, and did allow for some internal blood delivery, the channels soon healed over entirely and failed to continue the blood supply. Early attempts were also made to graft a blood vessel from the aorta directly into the heart muscle to provide an internal source of blood. While some benefits were seen, the surgery was technically demanding and the procedure was eclipsed by the introduction of coronary artery bypass graft surgery.
To overcome these problems, Mahmood Mirhoseini and Mary M. Cayton suggest transmyocardial revascularization by using a high-powered CO.sub.2 laser to make the channels. Mirhoseini M., Cayton M. M., Revascularization of the Heart by Laser, J Microsurg 2:253, June, 1981. The laser forms each channel by vaporizing a passageway completely through the wall of the heart. The relatively clean channel formed by the laser energy prevents the channel from healing over, and the channel either closes by clotting at the heart's outer surface, due to exposure to air, or manual pressure can be applied until bleeding from the channel ceases. However, if bleeding cannot be stopped, or if bleeding resumes at a later time, the patient may require surgery or may die.
Generally, it is desired that the channels be made primarily within the heart's inner surface (endocardium) since the endocardium has a greater need of an alternative supply of blood than the heart's outer surface (epicardium). It would be desirable not to create too large a channel through the epicardium because the channel must clot and/or heal at the heart's surface to prevent copious blood loss due to the forceful pumping action of the heart. It would be desirable to produce a channel which is widest at the point the channel exits the inner surface of the heart chamber, admitting a larger a volume of blood and being less susceptible to clotting or healing.
The current laser devices used to perform transmyocardial revascularization are inefficient at creating desirably shaped channels within the endocardium. For instance, a high power (i.e., 1,000 watt) carbon dioxide laser, whose beam is focused at the heart's surface, can make a channel completely through the heart wall in one shot in approximately 50 milliseconds, during diastole, when the heart is momentarily at rest. The channel, however, is usually wider in the epicardium than in the endocardium, making clotting or healing at the heart's outer surface less secure and making closure at the heart's inner surface more likely.
The prior art also uses several mirrors to reflect carbon dioxide laser energy toward the tissue to be vaporized. Maintaining the proper alignment of these mirrors at all times, however, is difficult and inconvenient for the operator.
Further, the use of less powerful lasers whose energy can be transmitted through optical fibers, such as argon-ion have also been proposed. Lee G. et al., Effects of Laser Irradiation Delivered by Flexible Fiberoptic System on the Left Ventricular internal Myocardium, Am Heart J., September, 1983. However, if the laser energy is applied to make the channel completely through the heart wall, the laser must be operated for a longer period of time than if it were used only to form a channel through the endocardium. If the procedure cannot be completed during diastole, within approximately 0.6 seconds, between heartbeats when the heart's electrical activity is minimal, a life threatening arrhythmia may result, and damage to the heart muscle during its compression may occur.
The present invention provides an improved device and procedure which overcomes the above-discussed problems by combining mechanical energy with laser energy and enabling the laser energy to be emitted directly onto the tissue to be vaporized.